Abstract
Abstract. In this paper we present a readout circuit for capacitive micro-electro-mechanical system (MEMS) sensors such as accelerometers, gyroscopes or pressure sensors. A flexible interface allows connection of a wide range of types of sensing elements. The ASIC (application-specific integrated circuit) was designed with a focus on ultra-low noise operation and high analog measurement performance. Theoretical considerations on system noise are presented which lead to design requirements affecting the reachable overall measurement performance. Special emphasis is put on the design of the fully differential operational amplifiers, as these have the dominant influence on the achievable overall performance. The measured input referred noise is below 50 zF/Hz within a bandwidth of 10 Hz to 10 kHz. Four adjustable gain settings allow the adaption to measurement ranges from ±750 fF to ±3 pF. This ensures compatibility with a wide range of sensor applications. The full input signal bandwidth ranges from 0 Hz to more than 50 kHz. A high-precision accelerometer system was built from the described ASIC and a high-sensitivity, low-noise sensor MEMS. The design of the MEMS is outlined and the overall system performance, which yields a combined noise floor of 200 ng/Hz, is demonstrated. Finally, we show an application using the ASIC together with a CMOS integrated capacitive pressure sensor, which yields a measurement signal-to-noise ratio (SNR) of more than 100 dB.
Highlights
Capacitive sensors are widely used for the accurate measurement of physical quantities such as pressure, acceleration or orientation
In this paper we present a readout circuit for capacitive micro-electro-mechanical system (MEMS) sensors such as accelerometers, gyroscopes or pressure sensors
MEMS based accelerometer from Mir Enterprises Ltd.: the measurement performance of a complete highsensitivity, low-noise acceleration measurement system containing the readout IC (ROIC) from Fraunhofer IMS and the sensing element from Mir Enterprises will be demonstrated in Sect. 6. 2
Summary
Capacitive sensors are widely used for the accurate measurement of physical quantities such as pressure, acceleration or orientation. In contrast to sensors built from discrete mechanical elements, MEMS based solutions have suffered, and still suffer, from a significantly increased noise level and reduced measurement performance. 1. MEMS based accelerometer from Mir Enterprises Ltd.: the measurement performance of a complete highsensitivity, low-noise acceleration measurement system containing the ROIC from Fraunhofer IMS and the sensing element from Mir Enterprises will be demonstrated in Sect. The feedback capacitor Cint, together with the input differential capacitance C of the sensing element, determines the overall closed-loop voltage gain of the amplifier stage. The proposed sensor interface allows the connection of single-ended or fully differential capacitive sensors in full or half bridge configuration either with or without external reference capacitors, depending on the type and characteristics of the sensing element used
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